Study of Abiotic Factors Controlling Marine Ecosystem Dynamics and Formation of Anomalous Conditions in Coastal Waters of the Far East in the 80th Cruise of the R/V Professor Gagarinskiy

Abstract

On cruise 80 of the R/V Professor Gagarinskiy from June 15 to July 18, 2022, integrated hydrographic and hydrochemical studies were carried out in Avachinskiy Bay of the Kamchatka Peninsula, on the northeastern shelf of Sakhalin Island, and in Peter the Great Bay to assess current environmental risks in the coastal zone of key areas of Russia’s Far Eastern seas and, in particular, to study possible abiotic factors that caused the mass mortality of marine organisms in Kamchatka in fall 2020. Comprehensive observations were performed, including CTD, hydrochemical water sampling, moorings, and plankton and bottom sediment sampling. An increased nutrient content was found, both in subsurface and intermediate Pacific waters, in comparison with 1990s–2000s data. Intensive snowmelt on adjacent mountain slopes during the survey period showed the significant impact of continental runoff on the hydrochemical characteristics of Avachinskiy Bay waters, causing decreased salinity and significantly increased concentrations of nutrients and chlorophyll a in the coastal zone. The dynamics of mesoscale eddies ensures transport of coastal waters to the ocean over a distance of more than 100 nautical miles. The results suggest that the catastrophic phenomenon off Kamchatka, associated with anomalous harmful algae blooms, is due to conjugate biogeochemical and hydrographic factors: river runoff and intrusion of deep waters on the shelf caused by coastal wind and dynamic upwelling during the period of maximum warming and eutrophication of subarctic Pacific waters, as well as the orographic and topographic features of Avachinskiy Bay.